This invention relates to an ultrasonic horn assembly having one or more of its major stack components formed separately and subsequently fused together.
Ultrasonic horn assemblies are used to distribute ultrasonic energy in a variety of industrial processes. One example involves bonding of two thermoplastic sheets of material together in the manufacture of personal care products such as diapers. These assemblies have a number of distinct components, which are connected in a stack. In one arrangement these components may include a power excitation device known as a converter (or driver assembly), amplitude modification devices known as boosters, and an ultrasonically energized tool known as a horn, which contacts a work piece.
Heretofore ultrasonic horn assembly stack components have been connected to each other by use of a fully threaded, high strength steel stud. A drawback of this arrangement is that a high-pressure center contact area tends to form in the area immediately around the stud at the interface between the two stack components being connected. In particular, the clamping forces are concentrated in an area immediately around the stud. The clamping pressure at the interface holding these two components together is significantly greater immediately around the stud than it is at the periphery of the mating surfaces remote from the stud. As such, the clamping force that holds the components together degrades as one moves peripherally away from the stud. As ultrasonic energy is transmitted across this interface over time and during extended operation of the horn assembly, the variation in clamping force at the interface facilitates various wear phenomena. In particular, fretting and spalling due to friction between poorly mated assembly interfaces can occur, producing severe surface damage. And oxidation which converts titanium on the component surface to black, hard, brittle titanium oxide can occur. Fretting, spalling, and oxidation degrade the efficiency of energy transfer between the components, and require periodic disassembly to refinish the stack components at the interface therebetween. Furthermore, the interface between the components, even prior to any significant wear, is a source of energy loss during energy transfer across the interface, because any interface represents an impedance mismatch between components which expresses itself as the generation of heat.
In certain previous embodiments the interface between the primary booster and the horn is eliminated by having the primary booster manufactured integrally with the horn. A drawback of this arrangement is that the integral booster and horn is a relatively large component, the manufacture of which requires substantial machining from an especially large, more complex forging. Moreover, matching the resonant frequency of the booster to that of the horn is not possible when the horn and booster are integral.
Isolation ring shells are employed to mount ultrasonic horn assembly boosters to mounting housing for supporting the assembly in suspension. In one prior arrangement the isolation ring shell is connected to the booster using a fastening device such as a threaded stud. Wear can occur at the connection between the shell and the booster. Alternatively, isolation ring shells have been forged integrally with boosters. This, however, requires forging a relatively large complex preform requiring substantial machining. It also requires that the isolation ring shell be of the same metal as the booster, which does not permit the isolation ring shell to be manufactured from a more damping material than the booster material.
In response to the above difficulties and problems, the invention provides an ultrasonic horn assembly which has reduced maintenance requirements for stack component interfaces, which has reduced machining requirements upon manufacture, which employs components with pre-matched resonant frequencies, which has more efficient energy transfer between stack components, and which overall operates more efficiently due to matched frequencies.
Briefly, therefore, the invention is directed to an ultrasonic horn assembly for transporting ultrasonic energy to an operating location to apply the ultrasonic energy to at least one article at the operating location. The assembly has a first stack component having at least one transfer face, and a second stack component distinct from the first stack component, the second stack component having at least one transfer face adapted to engage the transfer face of the first stack component at an interface for transmitting ultrasonic energy from one of the first and second stack components to the other. There is a fusion zone at the interface integrally connecting the first and second stack components together, wherein the fusion zone comprises metallic fusion of the first stack component to the second stack component.
The invention is also directed to an ultrasonic horn assembly having a first stack component and an isolation ring shell for mounting the first component to a mounting housing and supporting the stack component in suspension, wherein the isolation ring shell is distinct from the first stack component and is connected to the first stack component at an interface. There is a fusion zone at the interface integrally connecting the isolation ring shell and the first stack component together, wherein the fusion zone comprises metallic fusion of the isolation ring shell to the first stack component.
In another aspect the invention is a method for manufacturing an ultrasonic horn assembly for transporting ultrasonic energy to an operating location to apply the ultrasonic energy to at least one article at the operating location. The method involves engaging a transfer face of a first ultrasonic horn assembly stack component with a transfer face of a second ultrasonic horn assembly stack component to define an interface between the stack components; and metallurgically fusing the transfer face of the first ultrasonic horn assembly stack component with the transfer face of a second ultrasonic horn assembly stack component to form a fusion zone at the interface between the stack components.
The invention is also directed to a method for manufacturing an ultrasonic horn assembly which method includes fitting an isolation ring shell onto a component of the ultrasonic horn assembly, which isolation ring shell is adapted for mounting the ultrasonic horn assembly component to a mounting housing and supporting the component in suspension, such that a surface of the isolation ring shell engages a surface of the component at an interface; and metallurgically fusing the isolation ring shell to the component to form a fusion zone at the interface.
Other features and advantages will be in part apparent and in part pointed out hereinafter.